Chip cards are often used in connection with host devices to provide certain functionality to the host device. One example of such a chip card is a memory card that can be connected to the host device to increase its memory space. Another example is a so-called SIM card that is connected to a mobile communication device and provides functionality for identifying and authenticating the user of the mobile communication device to a mobile communication network.
A chip card comprises a microcontroller which is usually supplied with power from a power supply of a host device via a specific interface. According to its specification, the interface between the host device and the chip card usually allows to supply voltages of defined values to the chip card. For instance, the specification ISO 7816-3 comprises three classes corresponding to supply voltages of 5 V, 3 V and 1.8 V. Moreover, the current that can be supplied to the chip card is usually limited to predetermined values.
In particular, the microcontroller of the chip card comprises at least one processor. The performance or calculation speed of the processor, which particularly depends on the clock rate provided to the processor, determines the current that is to be supplied to the processor. For this reason, the limitation of the current that can be provided via the interface between the host device and the chip card limits the performance of the processor.
Moreover, the microcontroller usually comprises non-volatile memory units, such as electrical erasable read only memory (EEPROM) units or flash memory units. Such a memory unit can be erased and reprogrammed by supplying a programming voltage to the memory cells of the memory unit. However, the programming voltage usually exceeds voltage supplied to the chip card by the host device. Therefore, a DC to DC converter is usually integrated into the microcontroller, which provides the programming voltage of the memory units. Such DC to DC converters increase the complexity of the microcontroller and may be difficult to implement, when there is a great difference between the supply voltage and the required programming voltage of a memory unit.